Effects of Electric Field and Neutral Wind on the Asymmetry of Equatorial Ionization Anomaly

Abstract

The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans‐equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24‐hr trans‐equatorial neutral wind profile is measured using the Second‐Generation, Optimized, Fabry‐Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low‐Latitude Ionospheric Sensor Network and several other networks in South America. A physics‐based numerical model, Low‐Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind.

Interhemispheric Asymmetry in Response of Low‐Latitude Ionosphere to Perturbation Electric Fields in the Main Phase of Geomagnetic Storms

“…It has been shown that the effects of perturbation meridional winds could reach to equatorial latitudes only after 20-24 hr of the commencement of the MP (Bauske & Prölss, 1997;Fuller-Rowell et al, 2002;Prölss, 1995). Thus, this storm provides clear evidence that PPEF alone can be sufficient to modulate TEC over low latitudes in episodic manner supported by background meridional winds (Khadka et al, 2018). Thus, this storm provides clear evidence that PPEF alone can be sufficient to modulate TEC over low latitudes in episodic manner supported by background meridional winds (Khadka et al, 2018).…”

“…Emphasizing the competing roles of meridional neutral winds and vertical E × B drifts during quiet time, Khadka et al (2018) have recently explained the asymmetry in EIA due to the presence of interhemispheric meridional under strong or weak E × B drift. In case if there were no background meridional winds the equatorial plasma fountain formed due to vertical E × B drift shall almost equally distribute the plasma in low-latitude regions in both the hemispheres.…”

“…A recent lucid review of literature by Yu et al (2019) provides scope of coupling and future challenges in understanding inner magnetospheric dynamics and its implications on ionosphere coupling processes at various scales and marks the field to be open for intense research across different research communities working on space weather. This can be possibly explained by transport of plasma from lower to higher latitudes starting from over equator toward poles supported by slower diffusion and pressure gradient process in presence of background meridional winds (Khadka et al, 2018). Unusual and anomalous sharp peaks are observed in GPS-TEC from 12 stations throughout the day as shown by black arrows in Figure 12b.…”

“…In a given seasonal background and meridional wind preconditioning (Khadka et al, 2018), PPEF can exhibit hemispheric asymmetry that could either be due to preconditioning or due to asymmetry residing in the variability of sources of PPEF. The ANN-based E × B drift model developed under the present study replicates the observed E × B drift patterns even during storms.…”

“…It needs to be investigated for its efficiency in the respective hemisphere of origin and effects across the dip equator. Recently, Khadka et al (2018) have illustrated the competing roles of seasonal meridional winds and weak/strong E×B drift around dip equator in producing such asymmetry during quiet time. This study aims to resolve the specific tasks of finding the impact of dominating PPEF on the electrodynamics of the equatorial and low-latitude TEC (Huang, 2008(Huang, , 2019 and resulting hemispheric asymmetry during the MP .…”